1. Field of the Invention
The present invention relates to a syndiotactic styrene-based resin composition having excellent heat stability. This invention is hereinafter referred to as the "first invention". The styrene-based resin composition of the first invention can be used widely and effectively as heat resistant structural materials and further as various industrial materials, mechanical part materials and so on for which heat resistance is required.
The present invention further relates to a fibrous molding (e.g. melt or wet extruded "spun" fibers) produced from syndiotactic polystyrene and, in particular, the composition of the first invention. These fibrous moldings are excellent in heat resistance, chemical resistance and so on and thus can be used effectively as a heat resistant fiber, a marine material, a material for use in production of apparatuses for chemicals, and so on. This invention is hereinafter referred to as the "second invention".
The present invention further relates to a "stretched" molding preferably produced from the composition of the first invention, which is excellent in heat resistance and mechanical strength and thus can be used in various applications, such as in production of electric materials, wrapping films, car parts and so on. This invention is hereinafter referred to as the "third invention".
The third invention relates to stretched styrene-based resin moldings and a process for the production thereof. More particularly, it is concerned with stretched styrene-based resin moldings which are excellent in heat resistance, solvent resistance, chemical resistance, electric insulating properties, mechanical strength, modulus of elasticity, dimensional stability and transparency, and consequently can be used in various applications; and a process for efficiently producing these stretched styrene-based resin moldings.
In a very preferred embodiment of the stretched resin invention a shaped article of a styrene-based polymer is prepared by drawing a styrene-based polymer having a mainly syndiotactic structure and a weight-average molecular weight of at least 100,000 and having at least 85% syndiotacticity in the racemic pentad as (determined by nuclear magnetic resonance spectrometric analysis using a carbon isotope). This material is excellent in the mechanical strength such as elastic modulus, impact strength and the like and heat resistance.
2. Description of the Related Art
Styrene-based polymers are generally divided into three groups depending on the configuration thereof: isotactic, syndiotactic and atactic. It is known that a styrene-based polymer having an atactic configuration is obtained by the usual radical polymerization method, and a styrene-based polymer having an isotactic configuration is obtained by using a Ziegler-type catalyst.
In general, styrene polymers which have been hitherto used are those having atactic configuration as obtained by radical polymerization. However, improvement in physical properties by stretching such atactic styrene polymers cannot be expected.
Styrene polymers having isotactic configuration are also known, and attempts to stretch them have been made (Kobunshi Kagaku (Polymer Chemistry) 21, 206 (1964)). However, a satisfactory stretching effect in such isotactic styrene polymers cannot be obtained because the rate of crystallization is slow and the main chain composed of carbon-carbon bonds in the styrene polymers has a spiral structure.
Applicants hereof have developed a styrene-based polymer having a syndiotactic configuration which is obtained by using a titanium compound and a water modified organoaluminum compound (Japanese Patent Application Laid-Open No. 104818/1987). See also U.S. Pat. No. 4,680,353. Styrene-based polymers having a syndiotactic configuration must be molded at elevated temperatures because they have an especially high melting point as compared with styrene polymers having the other configurations. However, molding at high temperatures causes a reduction in molecular weight due to thermal decomposition of the polymer and this results in a reduction of advantageous mechanical properties of the syndiotactic polymer.
Known methods to prevent reduction in mechanical properties due to thermal decomposition of styrene polymers during molding thereof, include adding a triphosphite, a diphosphite or a phenolic antioxidant to the styrene polymer (usually having an atactic configuration). However, these antioxidants commonly used in atactic polystyrene, evaporate or are thermally decomposed at the temperatures at which syndiotactic polystyrene is molded and, therefore, they cannot be used with syndiotactic polystyrene.
It has now been found that certain anti-oxidants can be added to a styrene polymer having a syndiotactic configuration to prepare a styrene-based resin composition having excellent heat resistance. Based on the findings, the first invention has been completed.
The second invention relates to a fibrous molding or "spun" fiber of a syndiotactic polystyrene composition and not particularly to a fibrous molding or fiber of the composition of the first invention. The fiber may be stretched to further enhance the properties of the fiber.
A fibrous molding has heretofore been produced from thermoplastic resins. Such thermoplastic resins include polyethylene, polypropylene, polyethylene terephthalate, polyamide and so on. None of these thermoplastic resins, however, are satisfactorily high in heat resistance, chemical resistance and so on. Moreover they have disadvantages in that many of them are adversely effected by steam while others are expensive.
A styrene-based polymer having a syndiotactic configuration has advantages in that the starting materials are inexpensive, the melting point is high and chemical resistance is excellent. However fibrous moldings (or fibers) retaining the advantageous properties thereof, have not been produced from such styrene-based polymers.
It has been found that a fiber produced from a styrene-based polymer having a syndiotactic configuration which contains the antioxidants of the first invention hereof, by various spinning methods, has the desired heat resistance and chemical resistance. Based on the findings, the second invention has been completed.
As noted above, mixing other resins, rubber, or inorganic fillers into polymers, or stretching, has been attempted for the purpose of improving thermal properties and mechanical properties of polymers. Particularly for a styrene-based polymer, these techniques are widely applied because styrene-based polymers are generally poor in impact resistance.
That is, the styrene-based polymer which has heretofore been in general use is obtained by radical polymerization, and its configuration is atactic and further it is amorphous. Thus the impact resistance and mechanical strength of the styrene-based polymer are not sufficiently high. In order to overcome these problems, other resins and so on have been compounded to the styrene polymer, but the effect of improvement is not sufficiently high. Moreover, since the styrene-based polymer is atactic configuration, an improvement of physical properties thereof due to strain-induced crystallization cannot be expected.
Also as noted above, attempts were made to stretch a styrene-based polymer the configuration of which is isotactic (Kobunshi Kagaku (Polymer Chemistry), 21, 206 (1964)). However, since the styrene-based polymer is slow in a crystallization rate and its crystal structure is spiral, a substantially sufficient stretching effect cannot be obtained.
The present inventors have made extensive investigations in order to overcome the above problems. In the course of the investigations, since a styrene-based polymer of high syndiotacticity which has been developed by the present applicant (Japanese Patent Application Laid-Open No. 104818/1987) has a high melting point (160.degree. to 310.degree. C.), compounding other resins and so on, or stretching has been attempted. For example, (1) blending a styrene-based polymer having a syndiotactic configuration and a thermoplastic resin (Japanese Patent Application Laid-Open No. 257950/1987), (2) a composition comprising a styrene-based polymer having a syndiotactic configuration and an inorganic filler (Japanese Patent Application Laid-Open No. 257948/1987), and so forth have been proposed.
However, the above compositions containing a styrene-based polymer having a syndiotactic configuration and the stretched product cannot be said to have satisfactory properties when thermal properties and mechanical strength of stretched films, bottles and so on in practical use as produced by film molding, blow molding and so on are taken into consideration.
Thus the third invention is intended to overcome the above problems and to provide a styrene-based resin composition having excellent heat resistance and mechanical strength by stretching film moldings of syndiotactic styrene polymers.
The third invention provides axial and biaxial sheets of defined composition and having been subjected to defined stretch rates.